Multi – metals

Litho plates must have two distinct and opposing areas, called oleophilic and hydrophilic, which are formed on the one surface. Initially, lithographers observed that certain plates accepted grease far more readily than others, whilst others were more easily dampened. For example, the images on zinc plates tended to spread and thicken and it was once necessary to have a relatively course grain to retain sufficient moisture to keep the non – image clean. The reverse was found to be the case with grained aluminium – work tended to sharpen and a fine grain was used as water was easily retained.

Therefore it was logically assumed that if an oleophilic material could be used for the image and a hydrophilic one for the non – image an ideal plate would be produced.

Although more expensive than other plates the multi – metal is still relatively inexpensive when compared to other printing surfaces. The matt chromium surface of approximately 1,5 microns is hard and friction resistant and will not oxidize readily and therefore gumming up is not necessary for short press stops. Whichever multi – metal plate is used, they will give extremely long runs and prove to be efficient and require little damping to reproduce high – quality work.

The selection of a particular plate must be governed by several factors, the principle being: length of run, whether the job is to be reprinted, cost, and reproduction quality.

The quality of reproduction is also important. In this context it must be remembered that although it is possible to reproduce fine halftones on the plate, the plate is not the end product and must print well on the press. This is where the damping qualities of the non – image areas play a major part. Often a printer may select a more costly long run plate, such as anodized deep – etch or tri – metals which are capable of printing fine – quality work for a relatively short run but where a high standard is the key factor.

Oral Practice

Topic. Advantages and Disadvantages of Offset Lithography and Letterpress Printing.

You are all students of Graphic Arts Department. You’d like to get the idea about kinds of printing and technological processes used to obtain the finished product, the most magic miracle of all miracles in the world the name of which is «Book».

I. Прослушайте или прочитайте информацию.

Letterpress is the oldest form of printing. This method was invented by Johannes Gutenberg 500 years ago. Letterpress is the most economical method of printing because it prints directly from metallic types. In the letterpress process the printing is performed by means of a raised surface: the type or blocks that are to be printed are raised above the non- printing areas.

Letterpress is used for printing of books, magazines, business forms, tickets and so on. Most of these products are not necessarily printed in letterpress but can also be produced by other printing methods. Letterpress uses a lot of image-carriers. They can be divided into metallic composition, different kinds of pictorial image-carriers which can combine type images with pictures and a number of different duplicate plates. Four kinds of duplicate plates can be used in letterpress; stereotypes, electrotypes, rubber-plates and plastic plates.

Electrotypes are the best duplicate plates. They are used for printing long runs with the highest quality and precision. Presses for letterpress printing may be divided into three groups: platen presses, flat-bed cylinder presses and rotary presses. Platen and flat-bed cylinder presses which can print from type forms are used for the production of shorter runs than rotary presses. Rotary presses can print much faster than platen and flat-bed cylinder presses and are therefore used for long runs.

Plane printing uses printing image-carriers on which the printing areas and the non-printing areas are in the same plane.

The principle of plane printing is based on the fact that grease and water do not mix. Non-printing surfaces receive water solution and printing areas must receive greasy ink and repel water. At present, offset lithography is the most important method of plane printing. It can produce many kinds of products. For example, books, magazines, newspapers, maps, package materials and so on. Offset lithography is an indirect printing method. In direct printing methods the printing image-carrier is inked and the resulting ink image is directly transferred, or impressed, into the printing stock where it becomes the printed image. In offset lithography the ink image is not transferred to the stock but applied to an intermediate surface called the blanket. From the blanket the ink image is then transferred again, now to the stock where it becomes the final printed image.

Numerous presses are used for offset printing. Some of them are made for printing of sheets and some – for printing of webs. Web presses are faster than sheet-fed ones.

II. Ответьте на вопросы, используя данные в скобках слова.

1. What kinds of duplicate plates for letterpress do you know?

(stereotypes, electrotypes, plastic plates, rubber plates).

2. What kinds of presses for letterpress do you know?

(platen, cylinder, rotary).

3. For what runs are electrotypes used?

(long).

4. What quality have electrotypes?

(highest).

5. What presses print faster: rotary or cylinder?

(rotary).

6. What kinds of production are printed by letterpress?

(books, magazines, business forms).

7. Where are printing and non – printing areas situated in plane printing?

(in the same plane).

8. What presses are used for offset printing?

(web presses, sheet-fed presses).

9. Where is the ink image applied in offset printing?

(blanket).

10. Where is the ink image transferred from the blanket?

(the printing stock).

III. Разделите текст на смысловые части.

IV. Озаглавьте каждую часть текста.

V. Сделайте короткие сообщения на тему «Высокая печать» по данным группам слов.

a. letterpress, invent, method of printing, use, print, produce;

b. image-carriers, divide into, duplicate plates, stereotype, electrotype, plastic plate, rubber plate, run;

c. rotary, flat-bed cylinder press, platen press, therefore, faster.

VI. Сделайте короткое резюме текста о высокой печати, используя выражения:

The subject of the text is……

It is necessary to point out…

Further I should like to say some words about…

VII. Ответьте на вопросы:

1. What products can offset printing produce?

2. What is the most important method of plane printing?

3. What is the principle of lithography?

4. Is offset lithography an indirect printing method?

5. What is the difference between direct and indirect printing methods?

6. What does the blanket serve for?

7. What machines work faster: web presses or sheet- fed ones?

VIII. Обменяйтесь репликами о плоской печати типа:

I think that…I suppose that….What is your opinion about…

IX. Составьте краткую аннотацию текста о плоской печати, используя выражения:

The subject of the text is…The text points out that….. It is shown that…The next part of the text is devoted to….The text also discusses….

X. Сделайте короткие сообщения о плоской печати, об офсетной печати, о машинах для плоской печати, используя данные группы слов.

a. plane, plane printing, grease, water, mix, printing, non- printing, surfaces, receive, repel;

b. indirect, ink image, transfer, apply, intermediate surface, blanket;

c. web press, sheet – fed press, print, fast.

XI. Выскажите свои соображения о достоинствах и недостатках высокой и плоской печати.